1. Field of the Invention
This invention relates to an device for tensioning a flexible printing plate on a plate cylinder of a rotary printing machine with tensioning rails which are respectively located at each of the two ends of the plate and are braced against the side walls of a cylinder channel. For the trailing end of the plate, there is a one-piece tensioning rail. In the central portion of the trailing tensioning rail there is a clamping member for the end of the plate. In the outer regions of the trailing tensioning rail there are elements for stretching or compressing the trailing end of the plate in the axial direction of the plate cylinder.
2. Description of the Prior Art
Prior art plate cylinders have included tensioning rail configurations for providing tension to the leading and trailing end of a printing plate as an intermediate region of the printing plate extends about the cylindrical surface of the plate cylinder. Some such plate cylinders have also included means for relative stretching and contracting of the trailing end of the plate in an axial direction of the plate cylinder.
One such device is generally disclosed in U.S. Pat. No. 3,903,796, in which there are assigned to the trailing or rear end of the plate, two tensioning or gripping rail pairs which combine to support and locate the rear end of the printing plate by means of adjusting screws. These two tensioning rail pairs can be moved circumferentially in order to tension the printing plate as well as in an axial direction relative to the plate cylinder. Thus, it is possible to stretch the rear end of the plate, for example, in the case of the so-called "narrow printing", so that an exact register is obtainable. On the other hand, it is also possible to compress or contract the rear end. However, with the rear tensioning or gripping rail being divided it is difficult, in practical operation, to prevent the tensioning rail consisting of several sections from causing the printing plate to buckle.
Another such device is generally disclosed in U.S. Pat. No. 4,712,476, which corresponds to German Laid Open Patent Application No. P 36 06 351.7. This device includes tensioning rails operatively associated with both ends of the plate which are braceable against the side walls of a transverse or axial channel formed in the plate cylinder for tensioning of the printing plate. There is included an apparatus for selectively stretching and compressing at least one of the ends of the printing plate in an axial direction of the plate cylinder. The tensioning rail operatively associated with the one plate end is of a one-piece construction and has a clamping member which is disposed at a middle region thereof. Respective tensioning segments are disposed at the end regions of the tensioning rail and are actuable for stretching and/or compressing the one plate end. Specifically, the clamping elements for the outer edges of the one plate end include a pivotally mounted member having a circular clamping face for clamping the outer region between an axially slideable clamping backing element mounted on the tensioning rail. Pivotal movement of the clamping element is produced by some type of actuator which rotates the clamping element. Minor rotation of the clamping element moves the outer region of the one plate end and produces corresponding sliding movement of the clamping backing element.
Another device in U.S. Pat. No. 4,596,188 employs hydraulic piston means for moving and locating clamping devices therein. German Pat. No. DE-OS 32 28 244; DE-PS 28 57 614; DE-PS 32 22 022; and DE-GM 72 19 684 disclose other printing devices. These German Patents and U.S. Pat. Nos. 3,903,796; 4,596,188; and 4,712,476, are incorporated by reference as if included in their entirety herein.